The principle of cutting or working on substances by producing a plasma (or highly ionized gas) is not novel per se. Plasma may be created by passing a gas through an electric arc. The electrical energy in the arc is converted into thermal energy in the gas, after passing through the electric arc the gas appears in the form of a partially ionized plasma at high temperature. In medicine, experimental plasma scalpel prototypes have been made using two coaxial electrodes, with an outer anode forming a nozzle and an inner cathode terminating at a point which is set back slightly from the end of the outer anode. A flow of gas running along the inside space thus provided between the outer electrode and the inner electrode passes through the electric arc produced at the ends of the electrodes and leaves in the form of a high temperature plasma. This disposition is shown in the diagram of FIG. 1 where the nozzle-shaped outer anode 1 and needle-shaped inner cathode 2 can be seen. A degree of electric arcing is symbolized by dashed lines 3, and a flow of gas by arrows 4, together with plasma output 5. A prototype plasma scalpel of this type was developed by Link et al at the University of Purdue in 1970. The high temperature plasma jet coming from the nozzle of this prototype plasma scalpel is generated by passing argon through a D.C. electric arc. The electric arc is struck by putting the two electrodes into contact. The average plasma temperature at the outlet from the nozzle is approximately 3,000.degree. C.
This prior art device nevertheless suffers from several drawbacks. While plasma is being produced, the anode reaches very high temperatures and requires considerable cooling, while the cathode does not require so much cooling. The use of a system which propels the arc by means of a jet of gas well beyond the electrodes spreads out the volume occupied by the phenomenon, thereby making it impossible to reach very high temperatures; cooling due to the effect of the gas expanding together with the very fast natural cooling of the plasma where no longer excited appear to be the causes of this phenomenon. The use of a rare gas is becoming less and less common since rare gases are expensive and have a poorer heat transfer coefficient.
Preferred implementations of the present invention provide a device and a method of cutting or treating hard to soft substances, and in particular living tissue, which method and device are different in design from the prior art methods and devices in this field, in particular for obtaining greater safety in use and very accurate localization, together with a degree of versatility. The invention is essentially concerned with a tool or instrument that can be operated by hand, and preferably with one hand only.